Question: In physics class, the girl to boy ratio is $10$ to $4$. If there are a total of $28$ students, how many girls are there?
A ratio of $10$ girls to $4$ boys means that a set of $14$ students will have $10$ girls and $4$ boys. A class of $28$ students has $2$ sets of $14$ students. Because we know that there are $10$ girls in each set of $14$ students, the class must have $2$ groups of $10$ girls each. There is a total of $20$ girls in physics class.